Why would they?
- IPv6 is basically an abandoned standard. I wouldn't expect them to support gopher either.
- Residential ISP support for ipv6 is spotty, and anyone who does offer ipv6 offers ipv4 as well.
- When it is supported, ipv6 tends to be substantially slower than ipv4 in practice.
- The addresses are a pain to look at and work with.
- You now have twice as many things to fail.